eggs that she manages to lay. Only
when the queen dies is the taboo lifted-
and then only for a few individuals.
But now a second crisis arose. The
candidate royals began to quarrel among
themselves for control. They converged
on the brood chambers and jostled for
position there. They struggled to climb
on top of their rivals. The winners in
these encounters seized their opponents'
legs and antennae and dragged them
away. Unlike their thousands of ordi-
nary nest mates, they recognized one
another as individuals. In time a domi-
nance hierarchy formed, similar to a
pecking order among chickens and rank
orders among wolves. The Trailhead fe-
male who emerged as the alpha con-
tender-in other words, the one who
was able to chase away all her rivals-
won the reproductive role. Egg-laying
and larval growth resumed in a reduced
but orderly manner.
If the Trailhead Colony could not
understand the history of its own spe-
cies, how much did it understand of its
current condition? How could it make
the right decisions for survival? In fact,
the Trailhead Colony knew a great deal.
Worker ants are far more than auto-
mated specks running around on the
ground. Even with a brain one-mil-
lionth the size of a human's, an ant can
learn a simple maze half as fast as a lab-
oratory rat, and remember the direc-
tions to as many as five different desti-
nations when she forages away from the
nest. After exploring a new terrain, a
worker can integrate all the seemingly
haphazard twists and loops she made
and, amazingly, return to the nest in a
straight line. She can learn and recall the
special odor of the colony to which she
belongs. The Trailhead Colony, when
all the learning and thought of its work-
ers came together, was very smart, by in-
sect standards-and, with the unifying
power of its Qyeen lost and its popula-
tion growth plummeting, it needed to
call on that group intelligence to regain
its balance.
When one of the soldier-queens
dominated its rivals and became the new
queen, the recovery of the colony seemed
to be under way. A stream of eggs was
laid. Larvae began to :fill the empty brood
chambers. Their odor and hunger signals
joined with the pheromones of the new
Soldier-Qyeen and spread through the
60 THE NEW YORKER, JANUARY 25, 2010
nest. The power was returning. More
foragers took the field.
The renewed activity was short-lived,
however. The colony was doomed by a
hereditary trait even more basic than the
altruism of the workers and the phero-
monal ties that bound them together.
The T railheaders, along with all ants of
all kinds that have ever existed, back to
the birth of ants, in the late Jurassic pe-
riod, used a strange but elegant genetic
method to fix the sex of an individual at
birth. Fertilized eggs develop into fe-
males, which can become queens or
workers, and unfertilized eggs develop
into males, which can do nothing but
inseminate females. The Soldier-Qyeen
had never mated. Her children all arose
from unfertilized eggs and were there-
fore male drones, contributing nothing
to the welfare of the colony. They had
weak mandibles and small brains but
huge eyes and genitalia. They were
wondrously adapted for mating after
flying up in the air with virgin queens,
but even if they managed to accom-
plish this it would do nothing for the
Trailhead Colony. The males created by
the Soldier-Qyeen would not mate with
her or with other potential soldier-
queens. They were programmed to
mate only during nuptial flights away
from the nest.
Noway out existed for the Trailhead
Colony. The linchpin of its existence
was gone and could not be replaced.
The colony could for a while contribute,
through its production of males, to the
gene pool of the population of colonies
all around it, and in that way eke out one
last bit of Darwinian profit. But it could
do nothing more for its own physical
existence. With each passing day it be-
came more vulnerable. Its territory and
even its flesh were coveted by others.
Neighboring colonies were likely to
learn of its decline, and when that hap-
pened there would be war.
T;'or years, the Trailhead nest had been
r protected bya ten-thousand-member
force. Fifteen per cent of its adult mem-
bers were soldiers. A soldier's exoskele-
ton, twice the size of that of an ordinary
worker, is literally heavy armor: thick,
tough, and pitted in places for resilience
and strength. A pair of spines project
backward from the midsection of the
body to protect the waist. Spikes protect
the neck, and the rear margin of the head
is curved forward, forming a helmet.
When attacked, the soldier can pull in her
legs and antennae and tighten up the seg-
ments of her body, turning her entire sur-
face into a shield. The ordinary Trailhead
workers, while built for labor, were also
available for combat. They served as the
light infantry, using the swiftness and the
agility of their supple bodies to dart in and
out of enemy lines, seizing any leg or an-
tenna available, and holding onto it until
their nest mates could close in and grab
another body part. When the adversary
was finally pinned and spread-eagled,
others piled on to bite, sting, or spray her
with poison.
But now the number of able-bodied
adults had begun to dwindle, and the
survivors were growing old. The decline
of the colony was being observed by its
closest neighbor, the Streamside Colony,
a younger and now more powerful super-
organism. Early one morning, an élite
Streamside worker, followed by a squad
of her nest mates, left her home to assess
the strength of the Trailhead Colony.
(About ten per cent of the worker force
in any colony earns élite status, by initi-
ating more tasks and working harder and
more persistently than the other ants.)
.fu the élite scout left on her journey, she
remembered the route more or less pre-
cisely. She had been to the Trailhead ter-
ritory before, and she carried a compass
in her head, using the sun as a lodestar.
This reliance on the sun could have been
the source of a huge error for an ant, be-
cause the sun travels across the sky, its
angle constantly changing. However,
each ant also has a biological clock, set to
the twenty-four-hour cycle and run with
a precision far beyond the capacity of an
unaided human brain. Using her clock,
the scout was able to adjust her trajectory
and stay on track. She was also guided by
the prominent features of the landscape
that she had memorized during earlier
trips. A pair of pine seedlings were one
such signpost, a circular opening in the
canopy a second, a dark shadow beneath
a holly shrub a third. Then there was the
odor terrain, parts of which the scout had
memorized on earlier trips. As the
ground rushed by two millimetres be-
neath her body, she turned her antennae
downward, enough to almost touch the
earth, and swung them from side to side.
The odors she detected as she ran,